a(n) = 2*phi(n) if n composite, or 2*phi(n) - (A000120(n)-1) if n prime, where phi = A000010, Euler's totient function, and a(1) = 1.

A035532

a(n) = 2*phi(n) if n composite, or 2*phi(n) - (A000120(n)-1) if n prime, where phi = A000010, Euler's totient function, and a(1) = 1.

Terms

    a(0) =1a(1) =2a(2) =3a(3) =4a(4) =7a(5) =4a(6) =10a(7) =8a(8) =12a(9) =8a(10) =18a(11) =8a(12) =22a(13) =12a(14) =16a(15) =16a(16) =31a(17) =12a(18) =34a(19) =16a(20) =24a(21) =20a(22) =41a(23) =16a(24) =40a(25) =24a(26) =36a(27) =24a(28) =53a(29) =16

External references